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Epidermal growth factor and transforming growth factor alpha bind differently to the epidermal growth factor receptor
M E Winkler1, L O'Connor, M Winget
1Department of Medicinal and Biomolecular Chemistry, Genentech Inc., South San Francisco, California.
Abstract:
Epidermal growth factor (EGF) and transforming growth factor alpha (TGF alpha) compete with each other for binding to the EGF receptor. These two growth factors have similar actions, but there are distinguishable differences in their biological activities. It has never been clear how this one receptor can mediate different responses. A monoclonal antibody to the EGF receptor (13A9) has been identified which has only small effects on the binding of EGF to the EGF receptor, but which has very large effects on the binding of TGF alpha to the EGF receptor; 5 micrograms/mL antibody has been shown to totally block 0.87 microM TGF alpha from binding to purified EGF receptor and to lower both the high- and low-affinity binding constants of TGF alpha binding to EGF receptor on A431 cells by about 10-fold. The 13A9 antibody causes a 2.5-fold stimulation of the tyrosine kinase activity of partially purified EGF receptor, compared to a 4.0-fold stimulation of the tyrosine kinase activity by EGF under the same conditions. The data suggest either that the antibody stabilizes a conformation of the EGF receptor which is not favorable for TGF alpha binding or that it blocks a part of the surface of the receptor which is necessary for TGF alpha binding but not EGF binding.
Insights
A novel antibody (13A9) selectively inhibits transforming growth factor alpha (TGF alpha) binding to the epidermal growth factor (EGF) receptor. This suggests distinct receptor conformations mediate different growth factor signaling pathways.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Epidermal growth factor (EGF) and transforming growth factor alpha (TGF alpha) are ligands that bind to the EGF receptor.
- Despite similar actions, EGF and TGF alpha elicit distinct biological responses via the same receptor.
- The mechanism by which the EGF receptor mediates differential signaling remains unclear.
Purpose of the Study:
- To investigate the differential binding of EGF and TGF alpha to the EGF receptor.
- To characterize a monoclonal antibody (13A9) that targets the EGF receptor.
- To elucidate how the EGF receptor distinguishes between EGF and TGF alpha signaling.
Main Methods:
- Utilized a monoclonal antibody (13A9) against the EGF receptor.
- Assessed the effects of 13A9 on EGF and TGF alpha binding to purified EGF receptor and A431 cells.
- Measured the tyrosine kinase activity of the EGF receptor in response to EGF and TGF alpha with and without 13A9.
Main Results:
- The 13A9 antibody minimally affected EGF binding but significantly inhibited TGF alpha binding to the EGF receptor.
- 13A9 reduced TGF alpha binding affinity to the EGF receptor on A431 cells by approximately 10-fold.
- 13A9 stimulated EGF receptor tyrosine kinase activity by 2.5-fold, whereas EGF stimulated it by 4.0-fold.
Conclusions:
- The 13A9 antibody may stabilize an EGF receptor conformation unfavorable for TGF alpha binding.
- Alternatively, 13A9 might sterically hinder TGF alpha binding without affecting EGF binding.
- These findings suggest distinct receptor-ligand interactions mediate differential signaling by EGF and TGF alpha.